1. Field of the Invention
This invention relates to a method for producing steel filaments and more particularly to a method for producing heat treated continuous lengths of steel filaments.
2. Description of the Prior Art
Steel filaments are conventionally manufactured by preparing a melt of a specific composition, casting the melt, thermomechanically working the cast product and finally some technique of further reduction in cross-sectional area such as rolling, swaging or drawing. Intermediate annealing is frequently required to restore ductility in order to achieve substantial reductions in area. Generally speaking this technique is quite expensive because of low product yield and the numerous processing steps required to ultimately arrive at the final cross-section.
An alternate method for producing steel filaments is disclosed in co-pending patent application, "Method For Producing Wire With a Small Cross Sectional Area", Ser. No. 519,364 and assigned to the assignee of this invention. In this application steel filaments are produced by slitting coil stock having a microstructure substantially free of proeutectoid ferrite into ribbons having an aspect ratio less than 25. To obtain certain mechanical properties the slit product is thereafter heat treated. It has been found that heat treating fine filamentary material is expensive.
As used herein the terms "ribbon" and "filament" may be interchanged and define a steel product having a small cross-sectional area, i.e., less than 0.005 sq. in. (0.03226 cm.sup.2) with a cross-section that may be square, rectangular or round.
In U.S. Pat. No. 2,074,714 a method is disclosed for making wire from sheet metal. Sheet metal is rolled through a grooving mechanism so as to provide channels on opposite sides of a sheet which define the wires to be produced. The channels are subsequently separated by passing the sheet through a shearing apparatus thereby providing wirelike elements of polygonal cross-section. The disclosed process is suitable for producing stock for welding rods. It is well known in the art that fatigue strength and other mechanical properties are not important considerations for such products.
The method of the present invention produces continuous lengths of steel filaments with a small cross-sectional area having a heat treated microstructure by separating into segments pre-scored and heat treated steel coil stock.